1. Field of the Invention
The present invention relates to a semiconductor device having a circuit constructed of a thin film transistor (hereinafter referred to as TFT), and to a method of manufacturing the same. For example, the present invention relates to an electro-optical device, which is represented by a liquid crystal display device, and to electronic equipment loaded with the electro-optical device as a part.
Note that, in this specification, the term semiconductor device indicates general devices that function by utilizing semiconductor characteristics, and that electro-optical devices, semiconductor circuits and electronic equipment are all included in the category of the semiconductor device.
2. Description of the Related Art
In recent years, a technique for constructing a thin film transistor (hereinafter referred to as TFT) using a semiconductor thin film (on the order of several to several hundreds nm in thickness) formed on the substrate having an insulating surface is attracting attention. The TFTs are widely used for electronic devices such as an IC or an electro-optical device, and the development of a switching element for a liquid crystal display device is particularly urgent. In this specification, an electro-optical device is a synonym of a display device.
In the liquid crystal devices, an attention is paid on an active matrix liquid crystal display device in which, to obtain an image with high quality, pixel electrodes are arranged in matrix and the TFT is used as a switching element for connecting the respective pixel electrodes.
The active matrix liquid crystal display devices are roughly classified into two types. There are known a transmission type and a reflection type active matrix liquid crystal display devices.
The transmission type liquid crystal display device conducts display by adjusting the passing of light by emitting light from the back of the liquid crystal using back light and making use of the form birefringence and the optical activity of the liquid crystal. Further, the transmission type liquid crystal display device is further increasing in demand as a display for a mobile computer or a video camera.
Further, in the liquid crystal display device, TFTs having semiconductors made of amorphous silicon or poly silicon, are arranged in matrix, and a liquid crystal material is sandwiched between an active matrix substrate on which a pixel electrode connected to each TFT, a source wiring and a gate wiring each are formed, and an opposing substrate having an opposing electrode arranged oppositely thereto. Besides, a color filter for displaying colors is stuck on the opposing substrate, and polarization plates are arranged on the active matrix substrate and the opposing substrate, respectively, as optical shutters, to perform the color display.
This color filter has colored layers consisting of R (red), G (green), and B (blue), a light shielding mask for covering only gaps between pixels, and extracting a red color, a green color and a blue color by transmitting light therethrough. The light shielding mask is for making clear the screen. Further, the light shielding mask is generally constructed of an organic film containing a metallic film (chromium etc.) or a black pigment. The color filters are arranged at positions corresponding to the pixel, thereby being capable of changing the color of light to be extracted for each pixel. Note that, the position corresponding to the pixel means the position that accords with the pixel electrode.
In a conventional liquid crystal display device using a metallic film as a light shielding mask of a color filter, the problem in that a parasitic capacitance with other wirings is formed and delay in signals tends to occur. Further, in consideration of the environment, a non-chromium material is attracting attention. Furthermore, in the case that an organic film containing a black pigment is used as a light shielding mask of a color filter, a problem in that the manufacturing steps increase occurs.